Field
The present disclosure generally relates to firing green ceramic bodies and, more specifically, to firing cordierite green ceramic bodies.
Technical Background
Ceramic filters, particularly large frontal area filters, include organic raw materials that should be removed in the firing process. Such organic materials may be contained in, for example, binders (Methocel, polyvinyl alcohol, etc.), lubricants, dispersant, pore formers (starch, graphite, and other polymers). These materials may be burned out in the presence of oxygen at temperatures above their flash points. Some of these materials are also removed as volatile organic compounds (VOC) that are burned in a kiln and/or in an after treatment apparatus, such as a thermal oxidizer. The decomposition and/or oxidation of these materials usually release heat and often influence shrinkage or growth of the material, which may cause stresses and ultimately lead to cracking.
Conventional firing processes for large or heavy duty ceramic bodies rely on firing cycles with slow heating rates, such as 4° C./hr to 8° C./hr, when heating to a temperature below 600° C. These low heating rates allow the raw organic raw materials to be removed gradually and completely, thereby reducing the stress in the ceramic material. However, firing cycles are prolonged by using these low heating rates, as it may take up to 130 hours to heat the green ceramic body to 600° C., and, as a result, the entire firing cycle may take from 140 hours to 198 hours.
Accordingly, a need exists for a firing cycle with increased heating rates, particularly heating rates up to 600° C. that does not cause cracking in the ceramic body.